No abstract

Recent microwave reflection measurements of Josephson junction chains have suggested the presence of nearly coherent collective charge oscillations deep in the insulating phase. Here we develop a qualitative understanding of such coherent charge modes by studying the local dynamical polarizability of the insulating phase of a finite length sine-Gordon model. By considering parameters near the non-interacting fermion limit where the charge operator dominantly couples to solitonantisoliton pairs of the sine-Gordon model, we find that the local dynamical polarizability shows an array of sharp peaks in frequency representing coherent phase oscillations on top of an incoherent background. The strength of the coherent peaks relative to the incoherent background increases as a power law in frequency as well as exponentially as the Luttinger parameter approaches a critical value. The dynamical polarizability also clearly shows the insulating gap. We then compare the results in the high frequency limit to a perturbative estimate of phase-slip-induced decay of plasmons in the Josephson junction chain. arXiv:1811.07941v3 [cond-mat.supr-con]

A new Ba 2 CuO 4-y superconductor with critical temperature (T c) exceeding 70 K was discovered. The X-ray absorption measurement gives evidence that this cuprate resembles La 2 CuO 4 but is doped with a fairly large amount of holes, while in contrast to the so far known hole-doped high-T c cuprates, the new cuprate possesses a much shorter local apical oxygen distance as well as much expanded in-plane Cu-O bond, leading to unprecedented compressed local octahedron. In compressed local octahedron, the Cu3d3z 2-r 2 orbital level will be lifted above the Cu3dx 2-y 2 orbital level with more three-dimensional features, implying that pairing symmetry may carry admixtures from more than one gap, suggesting that Ba 2 CuO 4-y composed of alkaline earth copper oxides that are the essential elements to form cuprate superconductors may belong to a new branch of cuprate superconductors.